This nonprovisional application claims priority under 35 U.S.C. xc2xa7 119(a) on patent Application No. 2001-24592 filed in Republic of Korea on May 7, 2001, which is herein incorporated by reference.
1 . Field of the Invention
This invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device and a fabricating method thereof that is capable of increasing an aperture ratio and improving a repair efficiency at the same time. Also, this invention relates to a method of repairing a bad pixel by using the same.
2 . Description of the Related Art
Generally, a liquid crystal display (LCD) controls a light transmittance using an electric field to display a picture. To this end, the LCD includes a liquid crystal panel having liquid crystal cells arranged in a matrix type, and a driving circuit for driving the liquid crystal panel. The liquid crystal panel is provided with pixel electrodes for applying an electric field to each liquid crystal cell, and a common electrode. Typically, the pixel electrode is provided on a lower substrate for each liquid crystal cell, whereas the common electrode is integrally formed on the entire surface of an upper substrate. Each of the pixel electrodes is connected to a thin film transistor (TFT) used as a switching device. The pixel electrode drives the liquid crystal cell, along with the common electrode, in accordance with a data signal applied via the TFT.
Referring to FIG. 1 and FIG. 2, a lower substrate 1 of a conventional LCD includes a TFT T arranged at an intersection between a data line 4 and a gate line 2, a pixel electrode 22 connected to a drain electrode 10 of the TFT, and a storage capacitor S positioned at an overlapping portion between the pixel electrode 22 and the previous gate line 2xe2x80x2.
The TFT T includes a gate electrode 6 connected to the gate line 2, a source electrode 8 connected to the data line 4, and the drain electrode 10 connected, via a contact hole 20, to the pixel electrode 22. Further, the TFT T includes a gate insulating film (not shown) for insulating the gate electrode 6 from the source electrode 8 and the drain electrode 10, and semiconductor layers 14 and 16 for defining a channel between the source electrode 8 and the drain electrode 10 by a gate voltage applied to the gate electrode 6. Such a TFT T responds to a gate signal from the gate line 2 to selectively apply a data signal from the data line 4 to the pixel electrode 22.
The pixel electrode 22 is positioned at a cell area divided by the data line 4 and the gate line 2 and is made from a transparent conductive material having a high light transmittance. The pixel electrode 22 is formed on a protective layer (not shown) which is spread on the entire surface of the lower substrate 1, and electrically connected with the drain electrode 10 through the contact hole 20 formed on the protective layer. The pixel electrode 22 generates a potential difference from a common transparent electrode (not shown) provided at an upper substrate (not shown) by the data signal applied via the TFT T. By this potential difference, a liquid crystal positioned between the lower substrate 1 and the upper substrate (not shown) is rotated due to its dielectric anisotropy. Thus, the liquid crystal allows a light applied, via the pixel electrode 22, from a light source to be transmitted into the upper substrate.
The storage capacitor S is charged with a voltage in an application period of a gate high voltage to the previous gate line 2xe2x80x2 while discharging the charged voltage in an application period of a data signal to the pixel electrode, to thereby prevent a voltage variation in the pixel electrode 22. In this way, because the storage capacitor is used for having the pixel voltage remain stable, its capacitance value should be big enough. To this end, the storage capacitor S is formed in the manner of overlapping with the gate line 2xe2x80x2 as having a gate insulating film (not shown) therebetween.
In this liquid crystal display device, when there is used a normally white TN mode type liquid crystal, if a defect occurs at the channel between the source electrode 8 and the drain electrode 10 a problem occurs. The pixel cell is displayed as a brightness point because a voltage is not applied to the pixel electrode 22. Because the bad pixel cell, having the drain electrode 10 and the source electrode 8 opened, is brightly displayed, an observer of the bad pixel cell will readily notice it. Thus a repair will be needed so that the observer will not perceive the bad pixel cell.
One way to repair the bad pixel cell is to connect the neck part of the channel between the source electrode 8 and the drain electrode 10. The connection may be made by a laser, such that the data signal is always applied from the data line 4 to the pixel electrode 22. Another way to repair the bad pixel cell is to directly connect the pixel electrode 22 to the data line 4 by welding the pixel electrode 22 with the laser.
In this case, the neighbor pixel cells of the repaired bad pixel cell realize normal color, whereas the bad pixel cell does not receive the desired data such that it is not possible for the liquid crystal display device to realize the complete color.
In FIG. 2, there is shown a liquid crystal display device disclosed in Japanese Patent Laid-open Gazette No. Pyung 02-170614 (publication date: Jul. 12, 1990), having a repaired TFT RT besides a main TFT MT and having the channels of the MT and the RT separately formed.
Referring to FIG. 2, there are a main TFT MT positioned at the area below the pixel electrode 22 and horizontally in the middle of the pixel electrode 22, and a repair TFT RT positioned at the area between the data line 4 and the pixel electrode 22. The main TFT MT includes the source electrode 8 formed so as to extend in a perpendicular direction to the data line 4 (the gate line 2 direction) and the drain electrode 10 connected with the pixel electrode 22. Also, the repair TFT RT includes the source electrode 28 for repair, which is projected to form from the data line 4, and the drain electrode 30 for repair, which is not connected with the pixel electrode 22.
The main TFT MT responds to a gate signal from the gate line 2 to selectively supply a data signal from the data line 4 to the pixel electrode 22. The pixel electrode 22 is positioned at the cell area divided by the data line 4 and the gate line 2, and generates a potential difference from a common transparent electrode (not shown) formed on an upper substrate by the data signal supplied via the main TFT MT. By this potential difference, the liquid crystal located between the lower substrate and the upper substrate rotates due to its dielectric anisotropy, and an incident light from a light source is transmitted toward the upper substrate via the pixel electrode 22.
If a failure of the main TFT MT occurs, the data signal is not supplied to the pixel electrode 22 from the data line 4 by cutting between the source electrode 8 and the data line 4 of the main TFT MT. Then, the pixel electrode 22 is welded by the laser 50 so as to have the drain electrode 30 for repair connected with the pixel electrode 22. By this arrangement, the data signal from the data line 4 is supplied to the pixel electrode 22 through the repair TFT RT including the source electrode 28 for repair and the drain electrode 30 for repair. As a result, the bad pixel cell realizes the normal color.
The background art having such a TFT repair structure of the liquid crystal display suffers drawbacks.
For example, when repairing the bad pixel cell with a broken wire, the source electrode 8 of the main TFT MT is rather long, being formed along the gate line 2 from the data line 4. Due to this, a display area decreases. The display area decreases as much as the area where the source electrode 8 is formed of metal, such that an aperture ratio decreases. As a result, it becomes difficult to form the storage capacitor by overlapping the gate line 2 with the pixel electrode 22.
Also, because the source electrode 8 of the main TFT MT and the source electrode 28 of the repair TFT RT are formed at separate areas, this also works as a factor reducing the aperture ratio. That is, because two source electrodes 8 and 28 diverging from the data line 4 are necessary in one pixel area and the two source electrodes 8 and 28 need space for themselves, the size of the pixel electrode 22 diminishes relatively.
Moreover, in the TFT RT, as in FIG. 2, when the drain 30 for repair and the pixel electrode 22 are planarly separated, it is difficult to connect the drain electrode 30 and the pixel electrode 22 by the laser in order to repair it. Further, the gate electrode 6 or a semiconductor layer (not shown) can be damaged during the process.
It is an object of the present invention to address one or more of the drawbacks associated with the background art.
It is an object of the present invention to provide a liquid crystal display device and a fabricating method thereof for increasing a repair efficiency and an aperture ratio at the same time.
Another object of the present invention is to provide a method of repairing a bad pixel by using the liquid crystal display device.
In order to achieve these and other objects of the invention, a liquid crystal display device according to one aspect of the present invention includes a main thin film transistor having a common source electrode receiving a data signal, a pixel drain electrode opposed to the common source electrode as having a predetermined main channel between them and connected to a first pixel electrode for driving the liquid crystal of a first horizontal line, and a gate electrode responding to a scan signal and switching on/off the main channel; an auxiliary thin film transistor having the common source electrode in the main thin film transistor, a gate line applying the scan signal to the gate electrode, and a repair drain electrode opposed to the common source electrode as having a predetermined auxiliary channel between them and formed to overlap with a second pixel electrode for driving the liquid crystal of a second horizontal line; and an active layer forming the main channel and the auxiliary channel, the active layer extended from the main channel to the auxiliary channel through the common source electrode area.
The device further includes a gate insulating film formed to cover the gate electrode and the gate line on a substrate; a semiconductor layer formed on the gate insulating film; a protective layer formed on the entire surface of the gate insulating film to cover the common source electrode, the pixel drain electrode and the repair drain electrode; and a contact hole formed in the protective film to have the pixel drain electrode electrically in contact with the pixel electrode.
In the device, the semiconductor layer is formed at the neighbor area of the main thin film transistor, the auxiliary thin film transistor and a data line.
In the device, the semiconductor layer is formed at the neighbor area of the main thin film transistor and the auxiliary thin film transistor.
The device further includes a gate insulating film formed to cover the gate electrode and the gate line on a substrate; a semiconductor layer formed on the gate insulating film; a protective layer formed on the entire surface of the gate insulating film to cover the common source electrode, the pixel drain electrode and the repair drain electrode; and a contact hole formed in the protective film to have the pixel drain electrode electrically in contact with the pixel electrode.
In the device, the common source electrode, the pixel drain electrode and the repair drain electrode are patterned simultaneously as the semiconductor layer.
In the device, the semiconductor layer is formed at the neighbor area of the main thin film transistor, the auxiliary thin film transistor and a data line.
In the device, the semiconductor layer is formed at the neighbor area of the main thin film transistor and the auxiliary thin film transistor.
A method of fabricating a liquid crystal display device according to another aspect of the present invention includes the steps of forming a gate line and a gate electrode on a substrate; forming a gate insulating film on the substrate; forming a semiconductor layer on the gate insulating film; forming a data line and a common source electrode on the gate insulating film, and in addition, forming a pixel drain electrode and a repair drain electrode to oppose the common source electrode such that a main channel of a main thin film transistor and an auxiliary channel of an auxiliary thin film transistor reside in the semiconductor layer at the same time; forming a protective layer on the gate insulating film to cover the common source electrode, the pixel drain electrode and the repair drain electrode; and forming a pixel electrode on the protective film to overlap with the repair drain electrode and to be electrically in contact with the pixel drain electrode.
In the method, the gate electrodes of the main thin film transistor and the auxiliary thin film transistor are unified at the common source electrode area.
In the method, the semiconductor layer is formed at the neighbor area of the main thin film transistor, the auxiliary thin film transistor and the data line.
In the method, the semiconductor layer is formed at the neighbor area of the main thin film transistor and the auxiliary thin film transistor.
The method includes the steps of forming a gate line and a gate electrode on a substrate; forming a gate insulating film on the substrate to cover the gate electrode and the gate line; forming a semiconductor layer, a common source electrode and a data line by depositing a semiconductor material and a metal layer on the gate insulating film and patterning them at the same time, and in addition, forming a pixel drain electrode and a repair drain electrode to oppose the common source electrode such that a main channel of a main thin film transistor and an auxiliary channel of an auxiliary thin film transistor reside in the semiconductor layer at the same time; forming a protective layer on the gate insulating film to cover the common source electrode, the pixel drain electrode and the repair drain electrode; and forming a pixel electrode on the protective film to overlap with the repair drain electrode and to be electrically in contact with the pixel drain electrode.
In the method, the gate electrodes of the main thin film transistor and the auxiliary thin film transistor are unified at the common source electrode area.
In the method, the semiconductor layer is formed at the neighbor area of the main thin film transistor, the auxiliary thin film transistor and the data line.
In the method, the semiconductor layer is formed at the neighbor area of the main thin film transistor and the auxiliary thin film transistor.
A repairing method of a liquid crystal display device according to another aspect of the present invention includes the steps of connecting a pixel drain electrode for driving to a pixel electrode of a first horizontal line, and in addition, providing a thin film transistor including a repair drain electrode that overlaps with a pixel electrode of a second horizontal line; sensing a bad pixel included in the horizontal lines; opening a part of a drain electrode for driving of the bad pixel; and connecting the repair drain electrode to the pixel electrode of the bad pixel such that the same color data as a normal pixel, is supplied to the pixel electrode of the bad pixel.